Introduce for/a* and for/a expressions

conftest.py

@@ -1,7 +1,7 @@
 import _pytest
 import hy
 import os
-from hy._compat import PY3, PY35
+from hy._compat import PY3, PY35, PY36
 
 NATIVE_TESTS = os.path.join("", "tests", "native_tests", "")
 
@@ -10,7 +10,8 @@ def pytest_collect_file(parent, path):
             and NATIVE_TESTS in path.dirname + os.sep
             and path.basename != "__init__.hy"
             and not ("py3_only" in path.basename and not PY3)
-            and not ("py35_only" in path.basename and not PY35)):
+            and not ("py35_only" in path.basename and not PY35)
+            and not ("py36_only" in path.basename and not PY36)):
         m = _pytest.python.pytest_pycollect_makemodule(path, parent)
         # Spoof the module name to avoid hitting an assertion in pytest.
         m.name = m.name[:-len(".hy")] + ".py"

hy/_compat.py

@@ -22,6 +22,7 @@ import sys
 
 PY3 = sys.version_info[0] >= 3
 PY35 = sys.version_info >= (3, 5)
+PY36 = sys.version_info >= (3, 6)
 
 str_type     = str   if PY3 else unicode      # NOQA
 bytes_type   = bytes if PY3 else str          # NOQA

hy/compiler.py

@@ -1830,16 +1830,16 @@ class HyASTCompiler(object):
         return result
 
     @builds("for*")
+    @builds("for/a*", iff=PY35)
     @checkargs(min=1)
     def compile_for_expression(self, expression):
-        expression.pop(0)  # for
+        root = expression.pop(0)
 
         args = expression.pop(0)
-
         if not isinstance(args, HyList):
             raise HyTypeError(expression,
-                              "`for` expects a list, received `{0}`".format(
-                                  type(args).__name__))
+                              "`{0}` expects a list, received `{1}`".format(
+                                  root, type(args).__name__))
 
         try:
             target_name, iterable = args
@@ -1864,11 +1864,12 @@ class HyASTCompiler(object):
         body = self._compile_branch(expression)
         body += body.expr_as_stmt()
 
-        ret += asty.For(expression,
-                        target=target,
-                        iter=ret.force_expr,
-                        body=body.stmts,
-                        orelse=orel.stmts)
+        node = asty.For if root == 'for*' else asty.AsyncFor
+        ret += node(expression,
+                    target=target,
+                    iter=ret.force_expr,
+                    body=body.stmts,
+                    orelse=orel.stmts)
 
         ret.contains_yield = body.contains_yield
 

hy/core/macros.hy

@@ -108,11 +108,7 @@ used as the result."
      root)))
 
 
-(defmacro for [args &rest body]
-  "Build a for-loop with `args` as a [element coll] bracket pair and run `body`.
-
-Args may contain multiple pairs, in which case it executes a nested for-loop
-in order of the given pairs."
+(defmacro _for [node args &rest body]
   (setv body (list body))
   (if (empty? body)
     (macro-error None "`for' requires a body to evaluate"))
@@ -124,10 +120,26 @@ in order of the given pairs."
     (odd? (len args)) (macro-error args "`for' requires an even number of args.")
     (empty? body)     (macro-error None "`for' requires a body to evaluate")
     (empty? args)     `(do ~@body ~@belse)
-    (= (len args) 2)  `(for* [~@args] (do ~@body) ~@belse)
+    (= (len args) 2)  `(~node [~@args] (do ~@body) ~@belse)
     (do
       (setv alist (cut args 0 None 2))
-      `(for* [(, ~@alist) (genexpr (, ~@alist) [~@args])] (do ~@body) ~@belse))))
+      `(~node [(, ~@alist) (genexpr (, ~@alist) [~@args])] (do ~@body) ~@belse))))
+
+
+(defmacro for [args &rest body]
+  "Build a for-loop with `args` as a [element coll] bracket pair and run `body`.
+
+Args may contain multiple pairs, in which case it executes a nested for-loop
+in order of the given pairs."
+  `(_for for* ~args ~@body))
+
+
+(defmacro for/a [args &rest body]
+  "Build a for/a-loop with `args` as a [element coll] bracket pair and run `body`.
+
+Args may contain multiple pairs, in which case it executes a nested for/a-loop
+in order of the given pairs."
+  `(_for for/a* ~args ~@body))
 
 
 (defmacro -> [head &rest rest]

tests/native_tests/py36_only_tests.hy

@@ -0,0 +1,39 @@
+;; Copyright 2017 the authors.
+;; This file is part of Hy, which is free software licensed under the Expat
+;; license. See the LICENSE.
+
+;; Tests where the emitted code relies on Python ≥3.6.
+;; conftest.py skips this file when running on Python <3.6.
+
+(import [asyncio [get-event-loop sleep]])
+
+
+(defn run-coroutine [coro]
+  "Run a coroutine until its done in the default event loop."""
+  (.run_until_complete (get-event-loop) (coro)))
+
+
+(defn test-for/a []
+  (defn/a numbers []
+    (for [i [1 2]]
+      (yield i)))
+
+  (run-coroutine
+    (fn/a []
+      (setv x 0)
+      (for/a [a (numbers)]
+        (setv x (+ x a)))
+      (assert (= x 3)))))
+
+(defn test-for/a-else []
+  (defn/a numbers []
+    (for [i [1 2]]
+      (yield i)))
+
+  (run-coroutine
+    (fn/a []
+      (setv x 0)
+      (for/a [a (numbers)]
+        (setv x (+ x a))
+        (else (setv x (+ x 50))))
+      (assert (= x 53)))))